This invention relates generally to vehicle power systems, and more specifically, to direct current contactors.
Vehicles, such as aircraft, rely on contactors and relays for protection and control of opening and closing electrical power feed lines. A typical vehicle may contain a hundred or more contactors. In an alternating current voltage system, an electric current follows a waveform, typically a sine wave, and there exists a zero voltage cross over point on that waveform. If a contactor is opened at the cross over point, the arc problem described below that exists in direct current systems will not occur.
In a direct current voltage system, there is no zero voltage cross over point. If a set of DC contacts are opened, an electric arc will form in a gas-filled space between the contacts, and without intervention will continue until the space between the electrical contacts is too large to sustain the arc. An arc can produce a very high temperature and is undesirable in a vehicle power system, as it can damage a contactor and can decrease the life span of a contactor.
One solution to this problem is an arc chute. An arc chute is used to stretch an arc a sufficient distance so that the voltage cannot support the arc, and the arc will eventually break. However in a high voltage DC system, such a contactor becomes undesirably large due to the size required for the arc chute and the large spacing required between the contacts within the contactor.
Another solution to the DC arc problem is to create a hermetically sealed container to enclose the contacts. In this solution, the container is typically metal, and is typically soldered for an airtight seal. The container is then either hooked to a hard vacuum to remove air, or the container is filled with an inert gas. The absence of air decreases the distance that the arc can be maintained for the voltage in the atmosphere around the contacts. Side magnets are sometimes used in a hermetically sealed contactor to pull the arc and eventually break it. The hermetic cavity of the construction, however, makes the manufacture of the contactor difficult and costly.
There is a need for a low cost and/or non-hermetic contactor that can switch high voltage DC current with high reliability, preferably without the need for an arc chute.